Spark plug electrode

ABSTRACT

A spark plug electrode is made of a dispersion-strengthened nickel alloy containing small amounts of aluminum and, optionally, chromium.

United States Patent 1191 Weber Aug. 21, 1973 SPARK PLUG ELECTRODE2,071,645 2/1937 McNeil 75/170 3,323,911 6/1967 1 e [751 111mm" if?Rube" Weber Slutsburg, 3,370,942 2/1968 1:33,; 75/170 [73] Assignee:Westinghouse Electric Corporation,

Pittsburgh, Pa Primary Examiner-Richard 0. Dean Filed: Aug. 2,Att0rnyMal1l'iCe L- Pine] [21] Appl. No.: 168,364

[52] US. Cl 148/32, 75/170, 75/171 57 ABSTRACT [51] Int. Cl. C22c 19/00[58] Field of Search 75/170, 171, 128 R, v

75/128 E; 148/32 A spark plug electrode 1s made of adispersionstrengthened nickel alloy containing small amounts of [56]References Cited aluminum and, optionally, chromium.

UNITED STATES PATENTS 3,397,979 8/1968 Regester 75/170 8 Claims, N0Drawings SPARK PLUG ELECTRODE The present invention is directed todispersionstrengthened nickel alloy materials for use as spark plugelectrodes.

It has long been recognized that the metallic material employed as theelectrodes in spark plugs used in internal combustion engines haspresented a difficult metallurgical problem. It is also known thatsatisfactory performance of electrode material in a spark plug is amajor factor in satisfactory performance of the plug in the engine andis a critical factor not only in relation to the useful life of thespark plug itself, but also with relation to satisfactory performance ofthe engine. In spark plugs which are subjected to exceptionally severeservice, for example, in aircraft engines of high power output and evenin some racing car engines, the use of platinum and platinum alloys inthe electrodes has been advocated. Because of the high cost of platinumand its alloys, this solution is not available in relation to sparkplugs which are used in most automotive engines. Generally speaking,present-day automotive spark plugs employ electrodes made of high-nickelalloys such as an alloy containing about 2 percent manganese, about 2percent chromium, balance nickel or a nickelchromium-iron alloycontaining about 32.5 percent nickel, about 21 percent chromium, balanceessentially iron.

In service, spark plug electrodes are subjected to a severe combinationof conditions including spark erosion, attack due to the corrosiveconditions existing within the engine cylinder, elevated temperaturesand attack due to the presence of lead compounds in gasoline as well asother additives inserted in the gasoline. Electrode alloys are requiredto have relatively high thermal conductivity so as to prevent melting ofelectrode. Even if the conductivity of the alloy is sufficiently hightoprevent actual melting, alloys having lower conductivity operate athigher temperatures due to the resistance to the passage of electricitythere: through, thereby accentuating the effects of spark erosion andthe oxidation corrosion factors. It .is consid ered that the maximumtolerable resistivity for candidate electrode materials is about 50 to60 microhmcentimeters. It is desirable to provide alloys havingresistivity of a lower level so as to provide for cooler operatingtemperatures at the electrode especially at the electrode tips. a

The severe environment in which the electrodes must operate necessitateshigh corrosion resistance for candidate materials. Lead, halogens,sulfur, and vanadium in commercial fuels provide the major corrosiveagents in the form of lead sulfides, halides, sulfates,.and vanadiumpentoxide. Depending upon engine temperatures these corrosive compoundsmay exist as solids, liquids, or gases; the most severe corrosion occurswhen the electrodes are in contact with liquid corrosive media.

The presence of air mixed with the fuel produces an oxidizingenvironment. Electrode materials must have good oxidation resistance,especially under thennal cycling conditions. Another criterion is thatany oxide scale formed on the electrodes should not cause significantchange in the sparking characteristics. Hence, the desired oxidationbehavior for an electrode is to form an adherent oxide scale which doesnot inhibit spark- The conditions encountered in spark plug electrodesrepresent a severe combination of factors which are destructive to metalintegrity in service. Accordingly, the provision of spark plug electrodematerials which will operate satisfactorily in the engine environment isnot a matter of ready predictability.

With the advent of the mechanical alloying process as described, forexample, in the Benjamin US. Pat. No. 3,591,362, it appeared that a newway had become available whereby spark plug electrode materials havingsatisfactory properties could be prepared. Thus, the Benjamin procedureaffords a way whereby metallic material such as nickel-base alloys maybe provided with an extremely finely divided and well-distributed inertdispersoid together with desired alloying elements in controlledamounts, which alloying elements are extremely difficult to incorporatein nickel or nickel-base alloys by any other means, including powdermetallurgy.

The present invention is directed to the provision of special nickelalloy materials by mechanical alloying which may be employed as sparkplug electrode materials.

Generally, the invention comprises providing through the mechanicalalloying route dispersionstrengthened nickel alloy compositionscontaining, by

weight, about 0.1 percent to about 2.5 percent aluminum, up to about 6percent chromium, up to about 0.5 percent titanium, up to about 0.]percent carbon,up to about 1 percent of a metal from the groupconsisting of yttrium and Rare Earth metals, at least about 0.3 volumepercent and up to about 2.25 or 2.5 volume percent of a finely divided,well'distributed dispersoid oxide having a particle size of about toabout 1000 Angstroms from the group consisting of yttria, Rare Earthoxides, ceria and thoria. Preferably the dispersoid is yttria having aparticle size to about 200 to about SOOAngstroms present in the amountof about 0.3 percent to about 2.25 percent by volume. Especiallypreferred compositions from the standpoints of wire drawability andresistance to cyclic oxidation contain about 0.1 percent to about 1.5percent aluminum, up to about 4 percent chromium, and about 04 volumepercent to about 1 volume percent yttria and the balance essentiallynickel.

The special compositions are. prepared by the me chanical alloying routeto provide hard dense composite powders containing within each powderparticle essentially the desired composition and having a particle sizesufficiently coarse to resist atmospheric contami: nation upon exposure.Once the powder is produced it a is readily converted mm wire by hotcompacting, for example, by hot extrusion, followed by high reduction,

e.g., rolling to wire bar and hot or cold wire drawing. The materialdraws readily with reductions of up to 50 percent or 60 percent beingreadily accomplished between intermediate anneals. Intermediate annealsat temperatures in the range of about l,800 F. to 2,100 F. for times ofabout 1/2 to about 1 hour may be employed as needed when cold drawing isused for wire production.

The powder may initially be prepared by mechanical alloying, i.e., ahigh energy dry milling process performed in a mill, such as theattritor mill or other high energy mill as described in theaforementioned Benjas min patent, provided with a grinding mediumcharge, e.g., balls of steel, nickel or other material. Ball-topowderratios above l to l by volume preferably are employed with milling timesusually exceeding about hours and up to about 40 hours depending uponthe size of the mill. The mill may be operated using a sealed airatmosphere although other atmospheres such as nitrogen and nitrogen-airmixtures may be employed. Raw materials employed for the mechanicalalloying operation preferably include fine carbonyl nickel powder havinga size range of about 4 to about 7 microns. Aluminum may be introducedinto the initial powder mixture as a nickel-aluminum master alloy powdercontaining about 32 percent to about 46 percent aluminum. Chromiumpowder of high purity and having a particle size not exceeding about 200mesh may be employed. Other desired ingredients, e.g., titanium,yttrium, cerium, mischmetal, etc., in the initial powder mix may beadded directly or as master alloy powders. The powder mix is milled fora time sufficient to produce in the powder product a hardness ofsubstantially the saturation hardness for the material. In so doing,material from the starting powders is fragmented or comminuted and by acombination of repeated comminuting and welding factors are formed intonew composite powder products comprising fragments of initial startingmaterials bonded or welded into the form of dense metal particleswherein the dimensions across fragments of the original materialspresent in the composite powders becomes shorter and shorter as millingproceeds. It appears that the surface of the metal balls is the majorsite of the processing as material is welded to the ball surfaces and isbroken away again under the influence of the milling energy in the dryenvironment. Properly processed powder has an internal structure whichis so finely dispersed that at 250 diameters in the optical microscopeit is found that little evidence of individual phases remains. In thisway also, the dimension between individual particles of the hard oxidephase added to the initial powder mix becomes more and more closelyspaced, e.g., with interparticle spacings of less than 2 microns,preferably less than 1 micron, or even less, e.g., 0.5 microns. Thedispersoid particles themselves may be added in powder form directly tothe powder mix as fine powders having a dimension not exceeding about1,000 Angstroms. In the case of yttria, very fine material can beproduced by the calcination of yttrium oxalate. It is to be appreciatedthat when a sealed air atmosphere is employed in the attritor, somepick-up of oxygen from the atmosphere will occur in the product powder.Thus, oxygen contents as high as about 1 percent in the product powdermay result. This oxygen may be employed to produce a part or all of therequired oxide dispersoid in the consolidated material produced from thepowder by internal oxidation with reactive metallic elements present inthe product powder, including, for example, aluminum, titanium, yttrium,cerium, or other Rare Earth metals, etc. If desired, for purposes ofadjusting the total oxygen content of a product powder so as to conductinternal oxidation with the consolidated material to a desired extent,oxygen as a readily decomposable oxide, for example, nickel oxide, maybe introduced in small controlled amounts into the initial mix. Theshort spacings created in the product powder during the mechanicalalloying operation insure short distances for diffusion so that theoxygen atoms and reactive metal atoms, e.g., aluminum, yttrium, etc.,can react readily in the solid matrix so as to produce an extremelyfinely divided dispersoid.

The powder is preferably consolidated by hot extrusion. For thispurpose, the product powder can be canned in a metal can made of a metalsuch as mild steel or nickel and welded shut. Evacuation of the can isunnecessary. The can containing the metal powder is heated to atemperature within the range of about l,800 F. to about 2,l00 F. andextruded at an extrusion ratio between about 6 to l and 30 to l to forma consolidated bar. The can material can be moved from the extruded barby conventional means such as pickling and the bar can then be convertedto wire by conventional means.

In alloys provided in accordance with the invention, the particularlysignificant elements from the standpoint of oxidation resistance,including cyclic oxidation resistance, are aluminum and chromium. Theamounts of these elements are correlated to the amount of dispersoidemployed so as to insure drawability of the alloy. Preferably, at leastabout 0.1 percent aluminum is present. The aluminum content should notexceed about 2.5 percent in the interest of good cold drawability of thealloy. The chromium content does not exceed about 6 percent as otherwisethe resistivity of the alloy becomes undesirably high. For alloyscontaining about 1.5 percent to 2.25 percent, by volume, of a refractoryoxide dispersoid, chromium and aluminum should be limited to up to about1.5 percent and up to about 0.75 percent respectively in the interest ofcold drawability. When 6 percent chromium is present, the dispersoidcontent, e.g., yttria, should not exceed about 1 percent, by volume, inthe interest of cold drawability. Carbon is not intentionally added andpreferably is as low as possible to avoid deleterious effects, e.g., inrelation to drawability. Since carbon in small amounts may be present inraw material powders, titanium in small amounts may be employed to fixthe carbon as a carbide. The oxidation resistance of the alloy appearsto be improved by retaining a small amount of a metal such as cerium oryttrium in solid solution in the alloy.

In order to show those skilled in the art the special advantagesprovided in accordance with the invention, the following examples aregiven.

EXAMPLE I A 4.5 kilogram charge comprising carbonyl nickel powder arid0.6 parts by weight of fine yttria derived from the calcination ofyttrium oxalate were charged to a 4 gallon horizontal attrition millprovided with a horizontal shaft equipped with agitator anns extendingtherefrom to pass through the charge and charged with 200 pounds ofnickel balls with an average diameter of about 3/8 inch. The mill wasrun for l6 hours in a sealed air atmosphere with the agitator shaftoperating at 225 rpm. The powder produced was screened through -45 meshand sealed in a mild steel extrusion can. The resulting billet washeated to l,950 F. and ex truded at an extrusion ratio of 21.8 to l. Theresulting extruded bar stock was pickled to remove the steel canmaterial and was drawn from an initial diameter of 0.555 inches to afinal diameter of 0.093 inches. For intermediate anneals with the firstbeing conducted at l,900 F. and the last three being conducted at 2,000F. each for one hour were performed during the drawing operation. Thereductions before each anneal were respectively, 61.5, 64.5, 54.3 and54.5 percent with a total reduction of 97.2 percent being accomplished.The example shows that the foregoing alloy in accordance with theinvention, which contained 0.34 percent aluminum, 0.32 percent titanium,0.077 percent carbon, 3.8 percent chromium, and 0.8 percent yttria, byvolume, having an average particle size of 250 Angstroms, the balanceessentially nickel, was readily convertible to wire using conventionaltechniques. The aluminum, titanium and chromium were picked-up from theprevious run in the mill.

EXAMPLE II A kilogram powder batch proportioned to provide powdernominally containing 0.12 percent aluminum, 0.24 percent titanium, 0.06percent carbon, 2.5 percent thoria, by volume, with the balanceessentially nickel comprising carbonyl nickel powder and master alloysto introduce the aluminum and titanium was charged to a 10 gallonvertical attritor mill containing 375 pounds of nickel balls ofapproximately 3/8 inch diameter and was milled in a sealed airatmosphere for 24 hours with the impeller operating at 132 rpm. Thepowder thus produced was screened to 45 mesh and sealed in a mild steelextrusion can. The can was extruded at l,950 F. using an extrusion ratioof 16 to 1. Bar stock from this extrusion was drawn to wire by hotswaging followed by alternate drawing and annealing. It appeared thatthe swaging improved drawability slightly. The swaged bar which was 0.43inches in diameter reduced from an initial diameter of 0.65 inches wasthen drawn to 0.093 inch diameter wire with five intermediate anneals.Reductions of 36, 34.9, 31.6, 45.1, 45.9, and 45 percent wereaccomplished after each anneal at l,900 F. for one hour. A totalreduction of 97.8 percent was accomplished. It was found that thedrawing of this wire was limited to about 45 percent between anneals dueto the dispersoid level in the alloy.

EXAMPLE Ill The electrical resistivity of a number ofdispersionstrengthened wires produced in accordance with procedures suchas those set forth in Examples I and ll were determined together withthe resistivity for high purity nickel and for a nickel alloy containing2 percent manganese and 2 percent chromium which contain no dispersoid.The compositions and resistivities of the materials are set forth in thefollowing Table I.

TABLE I.--ELECTRICAL RESISTIVITY AT ROOM TEMPERATURE Composition (WeightPercent) Percent Percent (vo1.) Resistivity Alloy (micro- No. Al Ti 0 C1Y2Oa Th0; ohm cm.)

Balance of alloy is essentially nickel. "Alloy A also contained 1.9%manganese.

EXAMPLE 1v Material produced in accordance with Example ll, (Alloy No.I), together with material similarly produced and containing 0.03percent aluminum, 0.22 percent titanium, 0.044 percent carbon, 1.91percent chromium and 2.25 percent yttria, by volume, with the balanceessentially nickel (Alloy No. 6) were subjected to a cyclic oxidationtest together with material of similar dimension made of high puritynickel and made from commercially available TD nickel. The testatmosphere was air containing 5 percent water vapor and the testtemperature was 900 C. The test comprised 10 cycles of hours each attemperature followed by an air cool. At the conclusion of the test,samples were descaled abrasively using fine alumina powder, and werechecked for weight loss with the results set forth in the followingTable II.

TABLE II Alloy No. Descaled Wt. Loss (mg/cm) High Pun'ty Nickel 96 TDNickel l57 l l25 6 56 It was surprisingly found that the yttriatedmaterial (Alloy No. 6) exhibited superior cyclic oxidation resistance tothe thoriated material. It was also found that the Alloy No. 1 materialcontaining thoria and small amounts of aluminum and titanium exhibited alower weight lossthan did the commercial TD nickel material which isthoriated nickel containingthe same thoria content.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

I claim:

, l. A spark plug electrode made of an oxide dispersion-strengthened,corrosion resistant, nickel-base alloy, characterized by a goodcombination of (a) spark erosion resistance, (b) high thermalconductivity, (c) oxidation resistance under cyclic conditions and (d)cold drawability, said alloy consisting essentially, by weight, ofaluminum in an amount of about 0.1 percent with its upper limit notexceeding about 2.5 percent for purposes of cold drawability, up toabout 6 percent chromium,up to about 0.5 percent titanium, up to about0.1 percent carbon, up to about 1 percent of a metal from the groupconsisting of yttrium and Rare Earth metal and the balance essentiallynickel.

2. A spark plug electrode in accordance with claim 1 wherein thedispersoid is a refractory oxide selected from the group consisting ofyttria, Rare Earth oxides, ceria and thoria in an amount of about 0.3percent to about 2.5 percent, by volume, said alloy being characterizedin that when the volume of refractory dispersoid is within the range of1.25 to 2.25 percent, the aluminum and chromium are controlled so as notto exceed about 0.75 percent and 1.5 percent, respectively.

3. A spark plug electrode in accordance with claim 2 wherein the alloyis produced by mechanical alloying and the said dispersoid has aparticle size of about 100 to about 1000 Angstroms.

4. A spark plug electrode in accordance with claim 2 wherein the alloycontains about 0.1 percent to about 1.5 percent aluminum, up to about 4percent chromium, and about 0.4 volume percent to about 1 volume percentof yttria dispersoid.

5. An oxide dispersion-strengthened corrosion resistant nickel-basealloy characterized by a good combination of (a) spark erosionresistance, (b) high thermal condictivity, (c) oxidation resistanceunder cyclic conditions and (d) cold drawability, said alloy consistingessentially of, by weight, aluminum in an amount of about 0.l percentwith the upper limit not exceeding about 2.5 percent for purposes ofgood cold drawability, up to about 6 percent chromium, up to about 0.5percent titanium, up to about 0.1 percent carbon, up to about 1 percentof a metal from ghe group consisting of yttrium and Rare Earth metal andthe balance essentially nickel.

6. An alloy according to claim 5 wherein the dispersoid is a refractoryoxide selected from the group consisting of yttria, Rare Earth oxides,ceria and thoria in an amount of about 0.3 percent to about 2.5 percent,by volume, said alloy being characterized in that when the volume ofrefractory dispersoid is within the range of 1.25 to 2.25 percent, thealuminum and chromium are controlled so as not to exceed about 0.75percent and 1.5 percent, respectively.

7. An alloy according to claim 6 wherein the alloy is produced bymechanical alloying and the said dispersoid has a particle size of aboutto about 1000 Ang strorns.

8. An alloy according to claim 6 wherein the alloy contains about 0.1percent to about 1.5 percent aluminum, up to about 4 percent chromium,and about 0.4 volume percent to about 1 volume percent of yttriadispersoid.

. UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,753,795 Dated Auqust 21, 1972 inv mrw; JOHN HERBERT WEBER It iscertified that error appears in the above-identified patent A and thatsaid Letters Patent are hereby corrected as shown below:

After "Assignee: delete "Westinghouse Electric Corporation, Pittsburgh,Pa." and insert "The International Nickel -g Company, Inc. New York,N.Y.

Column 4, line 9, for "moved" read "removed" Column 4, .line 60, 'for"For" read "Four" Claim 5, line 11, for "ghe" read "the" Signed andsealed this 2nd day of July 1974.

(SEAL) Attest;

EDWARD M.F LETCHER,J R C. MARSHALL DANN Attesting Officer Commissionerof Patents

2. A spark plug electrode in accordance with claim 1 wherein thedispersoid is a refractory oxide selected from the group consisting ofyttria, Rare Earth oxides, ceria and thoria in an amount of about 0.3percent to about 2.5 percent, by volume, said alloy being characterizedin that when the volume of refractory dispersoid is within the range of1.25 to 2.25 percent, the aluminum and chromium are controlled so as notto exceed about 0.75 percent and 1.5 percent, respectively.
 3. A sparkplug electrode in accordance with claim 2 wherein the alloy is producedby mechanical alloying and the said dispersoid has a particle size ofabout 100 to about 1000 Angstroms.
 4. A spark plug electrode inaccordance with claim 2 wherein the alloy contains about 0.1 percent toabout 1.5 percent aluminum, up to about 4 percent chromium, and about0.4 volume percent to about 1 volume percent of yttria dispersoid.
 5. Anoxide dispersion-strengthened corrosion resistant nickel-base alloycharacterized by a good combination of (a) spark erosion resistance, (b)high thermal condictivity, (c) oxidation resistance under cyclicconditions and (d) cold drawability, said alloy consisting essentiallyof, by weight, aluminum in an amount of about 0.1 percent with the upperlimit not exceeding about 2.5 percent for purposes of good colddrawability, up to about 6 percent chromium, up to about 0.5 percenttitanium, up to about 0.1 percent carbon, up to about 1 percent of ametal from ghe group consisting of yttrium and Rare Earth metal and thebalance essentially nickel.
 6. An alloy according to claim 5 wherein thedispersoid is a refractory oxide selected from the group consisting ofyttria, Rare Earth oxides, ceria and thoria in an amount of about 0.3percent to about 2.5 percent, by volume, said alloy being characterizedin that when the volume of refractory dispersoid is within the range of1.25 to 2.25 percent, the aluminum and chromium are controlled so as notto exceed about 0.75 percent and 1.5 percent, respectively.
 7. An alloyaccording to claim 6 wherein the alloy is produced by mechanicalalloying and the said dispersoid has a particle size of about 100 toabout 1000 Angstroms.
 8. An alloy according to claim 6 wherein the alloycontains about 0.1 percent to about 1.5 percent aluminum, up to about 4percent chromium, and about 0.4 volume percent to about 1 volume percentof yttria dispersoid.